Electroluminescence (EL) devices using organic compounds are expected to be used for inexpensive full color display devices of the solid light emission type which can display a large area and development thereof has been actively conducted. In general, an EL device is constituted with a light emitting layer and a pair of electrodes faced to each other at both sides of the light emitting layer. When a voltage is applied between the electrodes, electrons are injected at the side of the cathode and holes are injected at the side of the anode. The electrons are combined with the holes in the light emitting layer and an excited state is formed. When the excited state returns to the normal state, the energy is emitted as light.
Heretofore, organic EL devices require higher driving voltages and show inferior luminance of emitted light and inferior efficiencies of light emission in comparison with inorganic devices. Moreover, properties of organic EL devices deteriorate very rapidly. Therefore, heretofore, organic EL devices have not been used practically. Although the properties of organic EL devices have been improved, organic EL devices exhibiting a sufficient efficiency of light emission and having sufficient heat resistance and life have not been obtained. For example, a phenylanthracene derivative which can be used for EL devices is disclosed in Japanese Patent Application Laid-Open No. Heisei 8(1996)-12600. However, an organic EL device using this compound exhibited an efficiency of light emission as low as about 2 to 4 cd/A and improvement in the efficiency is desired. In Japanese Patent Application Laid-Open No. Heisei 8(1996)-199162, an EL device having a light emitting layer containing a fluorescent dopant of a derivative of an amine or a diamine is disclosed. However, this EL device has a life as short as 700 hours at an initial luminance of emitted light of 300 cd/m2 although the efficiency of light emission is 4 to 6 dc/A and improvement in the life is desired. In Japanese Patent Application Laid-Open No. Heisei 9(1997)-268284, a material for EL devices having phenylanthracene group is disclosed. This material exhibits a marked decrease in the luminance of emitted light when the material is used at a high temperature for a long time and heat resistance is insufficient. Moreover, these devices do not emit light in the region of orange to red color. Since emission of red color is indispensable for the full color display by an EL device, a device emitting light in the region of orange to red color is desired. When these materials are used as the host material and other compounds are used as the doping material, a long life cannot be obtained. It is necessary for practical use that an initial luminance of emitted light of 10,000 d/m2 or greater be exhibited. However, this value has not been achieved. In Japanese Patent Application Laid-Open No. Heisei 11(1999)-152253, an example is disclosed in which a material for organic EL devices having a binaphthalene structure is added to a light emitting layer having the property to transfer electrons such as a layer of an aluminum complex or the like. However, in this example, the aluminum complex or the like emits light and the material for organic EL devices does not function as the light emitting center since the energy gap of the light emitting layer of the aluminum complex or the like is smaller than the energy gap of the material for organic EL devices.
Synthesis of arylamines used as a material for organic EL devices has been conducted by the Ullmann reaction using an amine and an iodobenzene. It is described, for example, in Chem. Lett., pp. 1145 to 1148, 1989; the specification of U.S. Pat. No. 4,764,625; and Japanese Patent Application Laid-Open No. Heisei 8(1996)-48974 that a triarylamine is produced by the reaction of a corresponding iodobenzene and a diarylamine in an inert hydrocarbon solvent such as decaline at 150° C. or higher in the presence of one equivalent or more of copper powder and a base such as potassium hydroxide as the typical example.
However, the process using the Ullmann reaction has drawbacks in that an expensive iodide must be used as the reacting agent, that the reaction cannot be applied to many types of compounds, that the yield of the reaction is not sufficient, that the reaction requires a temperature as high as 150° C. and a long time and that waste liquid containing a great amount of copper is formed since copper powder is used in a great amount and environmental problems arise.